FIG. 3 is a cross-sectional view showing a prior art amorphous solar cell. In FIG. 3, reference numeral 1 designates a substrate, numeral 2 designates as n type semiconductor layer provided over the substrate 1. Numeral 3 designates an i type semiconductor layer, numeral 4 designates a p type semiconductor layer, numeral 5 designates a transparent electrode, and numeral 6 designates a grid electrode. A semiconductor layer in an amorphous state or a micro-crystalline semiconductor layer is used for the n and p type semiconductor layers 2 and 4. A p or n type amorphous semiconductor including impurities has a high resistivity and a small energy band gap, and light absorption is likely to occur therein, thereby causing a loss in efficiency. Accordingly, micro-crystalline semiconductors have recently been used instead of amorphous semiconductors.
The device operates as follows.
When light is incident the surface of the transparent electrode 5, pairs of electrons and positive holes are generated in the i type amorphous semiconductor which electrons and positive holes are pulled towards the n and p type semiconductor layers 2 and 4, respectively, by an internal electric field due to the p and n type semiconductor layers 2 and 4. As a result, a larger number of electrons or positive holes than those arising from thermal equilibrium exist in the n and p type semiconductor layers 2 and 4, respectively. These extra electrons or positive holes flow into a load connected to the solar cell through an external circuit to thereby generate electric power.
In a solar cell using such an amorphous semiconductor, only the i type semiconductor layer 3 is considered to be a main generating region because electrons and positive holes generated in the p and n layer disappear quite rapidly due to recombination.
In order to overcome the disadvantages in such a prior art amorphous solar cell, it has been attempted to replace the amorphous semiconductor by a micro-crystalline semiconductor for the n and p type semiconductor layers 2 and 4, aiming at lowering the resistivity and increasing the energy band gap. In this case, however, recombination centers are produced at the boundary of the micro-crystalline layer and the amorphous layer, and the positive holes or electrons recombine with each other while the extra electrons and positive holes produced in the i layer are moving towards the n and p layers 2 and 4, respectively. This causes the problem that the photocurrent is reduced by the loss of the extra electrons and positive holes.
Another prior art amorphous solar cell is disclosed in an article by Y. Hamakawa, H. Okamoto and Y. Nitta, entitled "A new type of amorphous silicon photovoltaic cell generating more than 2.0 V", Applied Physics Letters, Vol. 35, pp 187 to 189 (1979). In this article a device is disclosed which is obtained by laminating a plurality of pin cells and effecting electrical connections between the adjacent cells by p/n junctions. In this device the p and n layers comprise amorphous silicon and recombination occurs in these amorphous layers.
Another prior art amorphous solar cell is disclosed in Japanese Laid-open Patent Publication No. Sho. 55-141765. In this solar cell, the electrical connecting layer between adjacent pin cells comprises a Pt cermet layer.